A known television tuner device will now be illustrated with reference to FIG. 2, which is a plan view of the layout of blocks in the television tuner device. A rectangular metal frame 21 having four side plates includes four compartments 25 to 28 separated by shielding plates 24. The compartment 25 contains a distributing unit, the compartment 26 contains a tuning unit, the compartment 27 contains a demodulating unit, and the compartment 28 contains a switching unit and a modulating unit. These circuit components are normally arranged a single printed-circuit board.
An input connector 22 for inputting a television signal and an output connector 23 for outputting the television signal distributed by the distributing unit are disposed on a short side plate 29 of the frame 21. Outer terminals 31 to 3, for power supply to each circuit component and input-output of signals, protrude from a first long side plate 30 contiguous to the short side plate 29. The distribution unit is disposed in the compartment 25 along the short side plate 29 to connect to the input connector 22, and the switching unit and the modulating unit are disposed in the compartment 28 along the short side plate 29 to connect to the output connector 23. The outer terminals 31 are disposed in the compartment 28 containing the switching unit and the modulating unit on the printed-circuit board.
The distribution unit disposed in the compartment 25 splits the input television signal into first and second television signal components and inputs the first television signal component to the tuner unit and the second television signal component to the switching unit. The tuner unit converts the first television signal component into an intermediate-frequency signal and outputs the intermediate-frequency signal to the demodulation unit. The demodulation unit demodulates the intermediate-frequency signal into a video signal and the like and outputs these signals to a video recorder (not shown in the drawing) through the terminals 33.
A video signal and the like from the video recorder are input to the modulating unit through the terminals 31, and are converted into a radio-frequency (RF) signal. The RF signal is then input to the switching unit. In a playback mode, the switching unit outputs the RF signal from the modulating unit to the output connector 23. Reproduced images are viewed on a television set (not shown in the drawing) having another television tuner device which is connected to the output connector 23. On the other hand, when the reproduced images are not viewed, the switching unit outputs the distributed signal directly to the output connector 23, and the received television signal can be visualized on the television set, as is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 10-32514.
As shown in FIG. 3, the tuning unit disposed in the compartment 26 includes an input-signal-tuning circuit 40 for receiving the (RF) television signal, a high-frequency amplifier 41, an interstage tuning circuit 42, and a mixer circuit 43 connected in series. The tuning unit further includes an oscillator 44 providing the mixer circuit 43 with an oscillation signal, a phase-locked-loop (PLL) circuit 45 controlling the oscillation frequency of the oscillator 44, and a reference-signal oscillator 46 which connects to a crystal oscillator 47 and provides the PLL circuit 45 with a reference signal oscillating at a reference frequency. The intermediate-frequency signal (IF) is output from the mixer circuit 43 to the terminals 32 in FIG. 2.
In the above-described television tuner device, since the tuning unit includes the crystal oscillator providing the PLL circuit with the reference signal, harmonics from the crystal oscillator interfere with the intermediate-frequency signal.